Most modern parking systems are partially or fully automated. For example, parking garages typically have entrance meters that allow a vehicle to obtain a ticket as the vehicle approaches the garage. Once the ticket is taken by the driver, the vehicle can enter the garage. Some systems also allow the driver to automatically pay a parking fee prior to leaving the garage.
As part of these automated systems, it is necessary to account for the total occupancy of the garage. For example, it is necessary to provide indicators when the garage is reaching capacity so that the number of vehicles that are allowed to enter the garage is controlled. Further, it can be important for revenue and accounting purposes to accurately account for the number of vehicles within the garage at given points in time.
While such systems typically attempt to track occupancy rates by monitoring the number of vehicles that enter and exit the garage, such systems can be less than optimal. For example, it is possible for multiple vehicles to enter the garage while being counted as a single vehicle (e.g., if one vehicle tail-gates another vehicle upon entry). In other situations, glitches in the entry and/or exit processes can result in inaccurate vehicle counts. Because of such inaccuracies, most parking systems are left with providing a rough estimate of occupancy rates at any given point in time.